1. Field of the Invention:
This invention relates to the art of manufacturing flat glass, wherein molten glass is delivered onto a surface of a pool of molten metal and formed while floating on the molten metal into a continuous sheet of glass. More particularly, this invention relates to devices positioned in the glass-supporting molten metal to control convection currents or flow of molten metal within the pool.
2. Brief Description of the Prior Art:
The use of dam barriers to influence thermal conditions within a glass-supporting pool of molten metal in a glass forming chamber has long been recognized. For example, U.S. Pat. No. 789,911 to Hitchcock discloses the use of a plurality of barriers to segregate a glass-supporting pool of molten metal into a plurality of pool segments, each of which could be selectively maintained at a desired temperature to permit the cooling and forming of glass as it passes over each segment of the pool during its travel through a forming chamber.
Many patents, including U.S. Pat. No. 3,317,302 to Misson, U.S. Pat. No. 3,584,475 to Galey and Sensi and U.S. Pat. No. 3,930,829 to Sensi, disclose dam barriers submerged in glass-supporting molten metal to alter or influence currents or flows in the molten metal. U.S. Pat. No. 3,930,829 to Sensi discloses that dam barriers may be used in pairs of "V" configurations to divert metal flows outwardly from the central portion of a pool of glass-supporting molten metal into marginal portions of the pool. The purpose given by Sensi for such an arrangement is to make the thermal conditions within the forming chamber more uniform across the width of the chamber.
U.S. Pat. No. 4,092,140 to Cerutti, Sensi and Henry discloses the use of triangular-shaped, closed loop heat pipes submerged in a glass-supporting pool of molten metal in a glass forming chamber. Such heat pipes would inherently divert flows of molten metal traveling in the direction of glass advance outwardly from the central portion of a forming chamber toward its marginal portions.
Dam barriers inhibit molten metal flows primarily by providing impenetrable bodies through which molten metal cannot flow so that the metal flows generally perpendicularly against dam barriers and is thus slowed and diverted to the extent that flow is maintained. Only incidently do they influence molten metal flows by a viscous drag effect since a dam barrier generally does not have any large surface area in contact with metal flowing tangential to it.
Modeling of glass forming processes has indicated that some short circuiting of molten metal flow over submerged dam barriers results in a fast flow of molten metal along with the advance of glass along its surface immediately adjacent the interface between the glass and the molten metal. This flow appears to reduce the effectiveness of submerged dam barriers. The present invention is therefore directed to an improved method and apparatus for the control of molten metal flows within the glass-supporting pool of molten metal.